System and method for sharing a control channel for carrier aggregation

ABSTRACT

A method for processing a control channel at a user agent (UA) to identify at least one of an uplink and a downlink resource allocated by a resource grant within a multi-carrier communication system wherein resource grants are specified by control channel element (CCE) subset candidates, the method comprising the steps of identifying the number of carriers used to communicate with the access device, based on the number of carriers used to communicate with the access device, identifying a number of CCE subset candidates to decode and decoding up to the identified number of CCE subset candidates in an attempt to identify the resource grant.

This application claims priority to U.S. provisional patent applicationNos. 61/187,070 which is titled “System and Method for Sharing a ControlChannel for Carrier Aggregation” which was filed on Jun. 15, 2009,61/258,525 which is “System and Method for Sharing a Control Channel forCarrier Aggregation” which was filed on Nov. 5, 2009 and 61/330,157which is titled “System and Method for Sharing a Control Channel forCarrier Aggregation” and which was filed on Apr. 30, 2010.

BACKGROUND

The present invention relates generally to data transmission in mobilecommunication systems and more specifically to methods for sharing acontrol channel for carrier aggregation.

As used herein, the terms “user agent” and “UA” can refer to wirelessdevices such as mobile telephones, personal digital assistants, handheldor laptop computers, and similar devices or other User Equipment (“UE”)that have telecommunications capabilities. In some embodiments, a UA mayrefer to a mobile, wireless device. The term “UA” may also refer todevices that have similar capabilities but that are not generallytransportable, such as desktop computers, set-top boxes, or networknodes.

In traditional wireless telecommunications systems, transmissionequipment in a base station transmits signals throughout a geographicalregion known as a cell. As technology has evolved, more advancedequipment has been introduced that can provide services that were notpossible previously. This advanced equipment might include, for example,an evolved universal terrestrial radio access network (E-UTRAN) node B(eNB) rather than a base station or other systems and devices that aremore highly evolved than the equivalent equipment in a traditionalwireless telecommunications system. Such advanced or next generationequipment may be referred to herein as long-term evolution (LTE)equipment, and a packet-based network that uses such equipment can bereferred to as an evolved packet system (EPS). Additional improvementsto LTE systems/equipment will eventually result in an LTE advanced(LTE-A) system. As used herein, the term “access device” will refer toany component, such as a traditional base station or an LTE or LTE-Aaccess device (including eNBs), that can provide a UA with access toother components in a telecommunications system.

In mobile communication systems such as E-UTRAN, an access deviceprovides radio access to one or more UAs. The access device comprises apacket scheduler for dynamically scheduling downlink traffic data packettransmissions and allocating uplink traffic data packet transmissionresources among all the UAs communicating with the access device. Thefunctions of the scheduler include, among others, dividing the availableair interface capacity between UAs, deciding the transport channel to beused for each UA's packet data transmissions, and monitoring packetallocation and system load. The scheduler dynamically allocatesresources for Physical Downlink Shared CHannel (PDSCH) and PhysicalUplink Shared CHannel (PUSCH) data transmissions, and sends schedulinginformation to the UAs through a scheduling channel.

Several different data control information (DCI) message formats areused to communicate resource assignments to UAs including, among others,a DCI format 0 for specifying uplink resources, DCI formats 1, 1A, 1B,1C, 1D, 2 and 2A for specifying downlink resources, and DCI formats 3and 3A for specifying power control information. Uplink specifying DCIformat 0 includes several DCI fields, each of which includes informationfor specifying a different aspect of allocated uplink resources.Exemplary DCI format 0 DCI fields include a transmit power control (TPC)field, a cyclic shift for demodulation reference signal (DM-RS) field, amodulation and coding scheme (MCS) and redundancy version field, a NewData Indicator (NDI) field, a resource block assignment field and ahopping flag field. The downlink specifying DCI formats 1, 1A, 2 and 2Aeach include several DCI fields that include information for specifyingdifferent aspects of allocated downlink resources. Exemplary DCI format1, 1A, 2 and 2A DCI fields include a HARQ process number field, an MCSfield, a New Data Indicator (NDI) field, a resource block assignmentfield and a redundancy version field. Each of the DCI formats 0, 1, 2,1A and 2A includes additional fields for specifying allocated resources.Other downlink formats 1B, 1C and 1D include similar information. Theaccess device selects one of the downlink DCI formats for allocatingresources to a UA as a function of several factors including UA andaccess device capabilities, the amount of data a UA has to transmit, thecommunication (channel) condition, the transmission mode to be used, theamount of communication traffic within a cell, etc.

DCI messages are synchronized with sub-frames so that they can beassociated therewith implicitly as opposed to explicitly, which reducescontrol overhead requirements. For example, in LTE frequency divisionduplex (FDD) systems, a DCI message for uplink resource is associatedwith an uplink sub-frame four milliseconds later so that, for example,when a DCI message is received at a first time, the UA is programmed touse the resource grant indicated therein to transmit a data packet inthe sub-frame four milliseconds after the first time. Similarly, a DCImessage for downlink resource is associated with a simultaneouslytransmitted downlink sub-frame. For example, when a DCI message isreceived at a first time, the UA is programmed to use the resource grantindicated therein to decode a data packet in a simultaneously receivedtraffic data sub-frame.

During operation, LTE networks use a shared Physical Downlink ControlCHannel (PDCCH) to distribute DCI messages amongst UAs. The DCI messagesfor each UA as well as other shared control information are separatelyencoded. In LTE, PDCCHs are transmitted in the first few OFDM symbolsover the whole system bandwidth, which can be called a PDCCH region. ThePDCCH region includes a plurality of control channel elements (CCEs)that are used to transmit DCI messages from an access device to UAs. Anaccess device selects one or an aggregation of CCEs to be used totransmit a DCI message to a UA, the CCE subset selected to transmit amessage depends at least in part on perceived communication conditionsbetween the access device and the UA. For example, where a high qualitycommunication link is known to exist between an access device and a UA,the access device may transmit data to the UA via a single one of theCCEs and, where the link is low quality, the access device may transmitdata to the UA via a subset of two, four or even eight CCEs, where theadditional CCEs facilitate a more robust transmission of an associatedDCI message. The access device may select CCE subsets for DCI messagetransmission based on many other criteria.

Because a UA does not know exactly which CCE subset or subsets are usedby an access device to transmit DCI messages to the UA, in existing LTEnetworks, the UA is programmed to attempt to decode many different CCEsubset candidates when searching for a DCI message. For instance, a UAmay be programmed to search a plurality of single CCEs for DCI messagesand a plurality of two CCE subsets, four CCE subsets and eight CCEsubsets to locate a DCI message. To reduce the possible CCE subsets thatneed to be searched, access devices and UAs have been programmed so thateach access device only uses specific CCE subsets to transmit DCImessages to a specific UA corresponding to a specific data trafficsub-frame and so that the UA knows which CCE subsets to search. Forinstance, in current LTE networks, for each data traffic sub-frame, a UAsearches six single CCEs, six 2-CCE subsets, two 4-CCE subsets and two8-CCE subsets for DCI messages for a total of sixteen CCE subsets. Thesixteen CCE subsets are a function of a specific Radio Network TemporaryIdentifier (RNTI) assigned to a UA 10 and vary from one sub-frame to thenext. This search space that is specific to a given UA is referred tohereinafter as “UA specific search space”.

In many cases it is desirable for an access device to transmit a largeamount of data to a UA or for a UA to transmit large amounts of data toan access device in a short amount of time. For instance, a series ofpictures may have to be transmitted to an access device over a shortamount of time. As another instance, a UA may run several applicationsthat all have to receive data packets from an access device essentiallysimultaneously so that the combined data transfer is extremely large.One way to increase the rate of data transmission is to use multiplecarriers (i.e., multiple frequencies) to communicate between an accessdevice and UAs, as is the case for LTE-A. For example, a system maysupport five different carriers (i.e. frequencies) and eight HARQprocesses so that five separate eight uplink HARQ and five separateeight downlink HARQ transmission streams can be generated in parallel.Communication via multiple carriers is referred to as carrieraggregation.

In the case of carrier aggregation, a control-channel structure isallocated to each carrier for distributing DCI control messages. As asimple way, each carrier can include a separate PDCCH region allowingcontrol channel information to be communicated between the access deviceand UAs for each carrier independently. This approach, while allowingfor control channel information to be distributed for each carrier,requires the allocation of a substantial amount of resources on eachcarrier. Furthermore, because the level of interference varies amongstcarriers, it may be difficult to implement PDCCH regions on all carriersequally. In some cases, for example, the interference levels on aparticular carrier may be so substantial as to make it difficult orimpossible to implement a PDCCH region on that carrier. Alternatively,the DCI message format for control messages on a first carrier may bemodified to provide an additional field for indicating a specificcarrier associated with each DCI message. This solution, however, isundesirable as it is currently undesirable to modify DCI formats.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram showing components of a communicationsystem including a user agent (UA) for sharing a control channel forcarrier aggregation;

FIG. 2 is an illustration of carrier aggregation in a communicationsnetwork where each component carrier has a bandwidth of 20 MHz and thetotal system bandwidth is 100 MHz;

FIG. 3 is an illustration of aggregation levels and search spaces thatmay be present within the PDCCH region;

FIG. 4 is a table showing aggregation levels for different UA-specificand common search spaces;

FIGS. 5 a and 5 b illustrate two exemplary PDCCH region design optionsfor implementing a control-channel for two or more carriers for carrieraggregation

FIG. 6 illustrates an exemplary PDCCH region having sets of CCEs,wherein each set of CCEs is assigned to a different carrier and alsoshows exemplary aggregation levels and search space for allocating DCIcontrol messages between carriers f1 and f2;

FIG. 7 illustrates an exemplary PDCCH region having CCEs allocated totwo carriers, wherein the CCEs allocated to each carrier may bedistributed through the PDCCH region and also shows exemplaryaggregation levels and search spaces that may be present within thePDCCH region for allocating DCI control messages between carriers f1 andf2;

FIG. 8 is an illustration of aggregation levels and search spaces thatmay be present within a PDCCH region wherein, for each aggregationlevel, the PDCCH candidates for a particular carrier may be shifted by amultiple of the number of CCEs in the next smaller aggregation level;

FIG. 9 is an illustration of aggregation levels and search spaces thatmay be present within a PDCCH region wherein the carrier index for aparticular PDCCH candidate may be calculated by a CCE index of the PDCCHcandidate;

FIG. 10 is a table showing aggregation levels for a UA-specific space,the size of each aggregation level in number of CCEs, and an extendednumber of PDCCH (CCE subset) candidates to be searched at eachaggregation level;

FIGS. 11 a-11 c illustrate Resource Element Group (REG) reordering,wherein the REG reordering may be used to distinguish amongst carrierspotentially associated with a PDCCH candidate;

FIG. 12 is an illustration showing example constructions of PDCCHcandidates for each of carriers f1 and f2 at aggregation levels 2, 4,and 8, wherein, for aggregation levels higher than aggregation level 1,the ordering of the CCEs that make up each potential PDCCH candidate isvaried;

FIG. 13 is a diagram of a wireless communications system including a UAoperable for some of the various embodiments of the disclosure;

FIG. 14 is a block diagram of a UA operable for some of the variousembodiments of the disclosure;

FIG. 15 is a diagram of a software environment that may be implementedon a UA operable for some of the various embodiments of the disclosure;

FIG. 16 is an illustrative general purpose computer system suitable forsome of the various embodiments of the disclosure;

FIG. 17 is a table showing aggregation levels for a UA-specific space,the size of each aggregation level in number of CCEs, and an extendednumber of PDCCH (CCE subset) candidates to be searched at eachaggregation level that are consistent with at least one embodiment ofthe present description;

FIG. 18 is a table showing aggregation levels for a UA-specific space,the size of each aggregation level in number of CCEs, and an extendednumber of PDCCH (CCE subset) candidates to be searched at eachaggregation level that are consistent with at least one embodiment ofthe present description;

FIG. 19 is a table showing aggregation levels for a UA-specific space,the size of each aggregation level in number of CCEs, and an extendednumber of PDCCH (CCE subset) candidates to be searched at eachaggregation level that are consistent with at least one embodiment ofthe present description; and

FIG. 20 is a table showing aggregation levels for a UA-specific space,the size of each aggregation level in number of CCEs, and an extendednumber of PDCCH (CCE subset) candidates to be searched at eachaggregation level that are consistent with at least one embodiment ofthe present description.

DETAILED DESCRIPTION

It has been recognized that a control channel may be shared amongst twoor more carriers in multi-carrier communication network systems.

At least some embodiments include a method for processing a controlchannel at a user agent (UA) to identify at least one of an uplink and adownlink resource allocated by a resource grant within a multi-carriercommunication system wherein resource grants are specified by controlchannel element (CCE) subsets, wherein each CCE subset is a controlchannel candidate, the method comprising the steps of identifying anumber of carriers used to communicate with the access device and basedon the number of carriers used to communicate with the access device,identifying a number of control channel candidates to decode.

In some cases the method further includes the step of decoding up to theidentified number of control channel candidates in an attempt toidentify the resource grant. In some cases there are at least first andsecond aggregation levels of control channel candidates where thecandidates include first and second different numbers of CCEs,respectively, and, wherein, the numbers of control channel candidatesare different for the first and second aggregation levels. In somecases, when only one carrier is used to communicate with the UA, a firstnumber of control channel candidates are identified and, when two ormore carriers are used to communicate with the UA, at least a secondnumber of control channel candidates are identified where the secondnumber is greater than the first number.

In some cases the identified number of control channel candidates formulti-carrier operation is at least equal to the number of candidatesfor single carrier operation. In some cases there are severalaggregation levels of control channel candidates and the identifiednumber of control channel candidates for multi-carrier operation is thegreater of the number of carriers times the number of aggregation levelsand the number of control channel candidates for single carrieroperation.

In some cases there are first, second, third and fourth aggregationlevels of control channel candidates, when only one carrier is used tocommunicate with the UA, the numbers of control channel candidates forthe first, second, third and fourth aggregation levels are A1, A2, A3and A4, respectively, and wherein, when two or more carriers are used tocommunicate with the UA, the numbers of control channel candidates forthe first, second, third and fourth aggregation levels are a function ofthe number of carriers used to communicate with the UA. In some cases,when two or more carriers are used to communicate with the UA, thenumbers C1, C2, C3 and C4 of control channel candidates for the first,second, third and fourth aggregation levels, respectively, aredetermined by solving the following equations C1=A1+B1×(N−1),C2=A2+B2×(N−1), C3=A3+B3×(N−1), C4=A4+B4×(N−1), where B1, B2, B3 and B4are scaling parameters.

In some cases A1, A2, A3 and A4 are 6, 6, 2 and 2, respectively.

Some embodiments include an apparatus for processing a control channelat a user agent (UA) to identify at least one of an uplink and adownlink resource allocated by a resource grant within a multi-carriercommunication system wherein resource grants are specified by controlchannel element (CCE) subset candidates, the apparatus comprising aprocessor programmed to perform the steps of identifying the number ofcarriers used to communicate with the access device, and based on thenumber of carriers used to communicate with the access device,identifying a number of control channel candidates to decode.

In some cases the processor is further programmed to perform the step ofdecoding up to the identified number of control channel candidates in anattempt to identify the resource grant. In some cases there are at leastfirst and second aggregation levels of control channel candidates wherethe candidates include first and second different numbers of CCEs,respectively, and, wherein, the numbers of control channel candidatesare different for the first and second aggregation levels. In somecases, when only one carrier is used to communicate with the UA, a firstnumber of control channel candidates are identified and, when two ormore carriers are used to communicate with the UA, at least a secondnumber of control channel candidates are identified where the secondnumber is greater than the first number.

In some cases the identified number of control channel candidates formulti-carrier operation is at least equal to the number of candidatesfor single carrier operation. In some cases there are severalaggregation levels of control channel candidates and the identifiednumber of control channel candidates for multi-carrier operation is thegreater of the number of carriers times the number of aggregation levelsand the number of control channel candidates for single carrieroperation.

In some cases there are first, second, third and fourth aggregationlevels of control channel candidates, when only one carrier is used tocommunicate with the UA, the numbers of control channel candidates forthe first, second, third and fourth aggregation levels are A1, A2, A3and A4, respectively, and wherein, when two or more carriers are used tocommunicate with the UA, the numbers of control channel candidates forthe first, second, third and fourth aggregation levels are a function ofthe number of carriers used to communicate with the UA. In some cases,when two or more carriers are used to communicate with the UA, thenumbers C1, C2, C3 and C4 of control channel candidates for the first,second, third and fourth aggregation levels, respectively, aredetermined by solving the following equations C1=A1+B1×(N−1),C2=A2+B2×(N−1), C3=A3+B3×(N−1), C4=A4+B4×(N−1), where B1, B2, B3 and B4are scaling parameters. In some cases A1, A2, A3 and A4 are 6, 6, 2 and2, respectively.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described. The followingdescription and the annexed drawings set forth in detail certainillustrative aspects of the invention. However, these aspects areindicative of but a few of the various ways in which the principles ofthe invention can be employed. Other aspects, advantages and novelfeatures of the invention will become apparent from the followingdetailed description of the invention when considered in conjunctionwith the drawings.

The various aspects of the subject invention are now described withreference to the annexed drawings, wherein like numerals refer to likeor corresponding elements throughout. It should be understood, however,that the drawings and detailed description relating thereto are notintended to limit the claimed subject matter to the particular formdisclosed. Rather, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theclaimed subject matter.

As used herein, the terms “component,” “system” and the like areintended to refer to a computer-related entity, either hardware, acombination of hardware and software, software, or software inexecution. For example, a component may be, but is not limited to being,a process running on a processor, a processor, an object, an executable,a thread of execution, a program, and/or a computer. By way ofillustration, both an application running on a computer and the computercan be a component. One or more components may reside within a processand/or thread of execution and a component may be localized on onecomputer and/or distributed between two or more computers.

The word “exemplary” is used herein to mean serving as an example,instance, or illustration. Any aspect or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs.

Furthermore, the disclosed subject matter may be implemented as asystem, method, apparatus, or article of manufacture using standardprogramming and/or engineering techniques to produce software, firmware,hardware, or any combination thereof to control a computer or processorbased device to implement aspects detailed herein. The term “article ofmanufacture” (or alternatively, “computer program product”) as usedherein is intended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. For example, computerreadable media can include but are not limited to magnetic storagedevices (e.g., hard disk, floppy disk, magnetic strips . . . ), opticaldisks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ),smart cards, and flash memory devices (e.g., card, stick). Additionallyit should be appreciated that a carrier wave can be employed to carrycomputer-readable electronic data such as those used in transmitting andreceiving electronic mail or in accessing a network such as the Internetor a local area network (LAN). Of course, those skilled in the art willrecognize many modifications may be made to this configuration withoutdeparting from the scope or spirit of the claimed subject matter.

In general, the inventive system and methods have been developed toshare a single control channel resource such as a Physical DownlinkControl CHannel (PDCCH) region amongst two or more carriers. As such,the system provides a multi-carrier control structure allowing downlinkcontrol information (DCI) control messages distributed via one PDCCHregion to determine resource allocations on one or more carriers. Ingeneral, the present system may be implemented using existing DCIcontrol message formats described above. As such, the lengths of theexisting DCI formats, even after implementation of the present system,may remain unchanged.

Referring now to the drawings wherein like reference numerals correspondto similar elements throughout the several views, FIG. 1 is a schematicdiagram illustrating an exemplary multi-channel communication system 30including a user agent (UA) 10 and an access device 12. UA 10 includes,among other components, a processor 14 that runs one or more softwareprograms wherein at least one of the programs communicates with accessdevice 12 to receive data from, and to provide data to, access device12. When data is transmitted from UA 10 to device 12, the data isreferred to as uplink data and when data is transmitted from accessdevice 12 to UA 10, the data is referred to as downlink data. Accessdevice 12, in one implementation, may include an E-UTRAN node B (eNB) orother network component for communicating with UA 10.

To facilitate communications, a plurality of different communicationchannels are established between access device 12 and UA 10. For thepurposes of the present disclosure, referring to FIG. 1, the importantchannels between access device 12 and UA 10 include a PDCCH 70, aPhysical Downlink Shared CHannel (PDSCH) 72 and a Physical Uplink SharedCHannel (PUSCH) 74. As the label implies, the PDCCH is a channel thatallows access device 12 to control UA 10 during downlink datacommunications. To this end, the PDCCH is used to transmit scheduling orcontrol data packets referred to as DCI packets to the UA 10 to indicatescheduling to be used by UA 10 to receive downlink communication trafficpackets or transmit uplink communication traffic packets or to sendspecific instructions to the UA (e.g. power control commands, an orderto perform a random access procedure, or a semi-persistent schedulingactivation or deactivation). A separate DCI packet may be transmitted byaccess device 12 to UA 10 for each traffic packet/sub-frametransmission.

Exemplary DCI formats include DCI format 0 for specifying uplinkresources and DCI formats 1, 1A, 1B, 1C, 1D, 2 and 2A for specifyingdownlink resources. Other DCI formats are contemplated. Exemplary DCIpackets are indicated by communication 71 on PDCCH 70 in FIG. 1.

Referring still to FIG. 1, exemplary traffic data packets or sub-frameson PDSCH 72 are labeled 73. The PUSCH 74 may be used by UA 10 totransmit data sub-frames or packets to access device 12. Exemplarytraffic packets on PUSCH 74 are labeled 77.

Carrier aggregation can be used to support wider transmission bandwidthsand increase the potential peak data rate for communications between UA10, access device 12 and/or other network components. In carrieraggregation, multiple component carriers are aggregated and may beallocated in a sub-frame to a UA 10 as shown in FIG. 2. FIG. 2 showscarrier aggregation in a communications network where each componentcarrier has a bandwidth of 20 MHz and the total system bandwidth is 100MHz. As illustrated, the available bandwidth 100 is split into aplurality of carriers 102. UA 10 may receive or transmit on multiplecomponent carriers (up to a total of five carriers 102 in the exampleshown in FIG. 2), depending on the UA's capabilities. In some cases,depending on the network deployment, carrier aggregation may occur withcarriers 102 located in the same band and/or carriers 102 located indifferent bands. For example, one carrier 102 may be located at 2 GHzand a second aggregated carrier 102 may be located at 800 MHz.

Referring to FIG. 3, an exemplary PDCCH region includes a plurality ofcontrol channel elements (CCEs) 110 that are used to transmit DCIformatted messages from access device 12 to UA 10. In the illustratedexample, the PDCCH region includes thirty-eight CCEs, however otherPDCCH instances may include more or fewer than 38 CCEs. Access device 12selects one or an aggregation of CCEs to be used to transmit a DCImessage to UA 10, the CCE subset selected to transmit a messagedepending at least in part on perceived communication conditions betweenthe access device and the UA. For instance, where a high qualitycommunication link is known to exist between an access device and a UA,the access device may transmit data to the UA via a single one of theCCEs (see 116) and, where the link is low quality, the access device maytransmit data to the UA via a subset of two (see 118), four (see 120) oreven eight CCEs (see 122), where the additional CCEs facilitate a morerobust transmission of an associated DCI message. The access device mayselect CCE subsets for DCI message transmission based on many othercriteria.

Hereinafter, unless indicated otherwise, CCE subsets that include oneCCE will be referred to as “Aggregation level 1” or AL1 subsets.Similarly, subsets that include two CCEs will be referred to as“Aggregation level 2” or AL2 subsets, subsets that include four CCEswill be referred to as “Aggregation level 4” or AL4 subsets, and subsetsthat include eight CCEs will be referred to as “Aggregation level 8” orAL8 subsets. A higher aggregation level indicates that the number ofCCEs used to transmit a particular DCI is larger (e.g., aggregationlevel 8 is higher than aggregation level 4) and is therefore more robustassuming a given set of channel conditions. Accordingly, UA's 10 withpoor channel conditions may be assigned higher aggregation levels toensure the UAs 10 can successfully decode DCI messages received onPDCCHs.

Referring now to FIG. 4, a table is provided that summarizes theinformation in FIG. 3 by showing aggregation levels for the UA-specificand common search spaces 114 and 112, respectively, the size of eachaggregation level in number of CCEs, and the number of PDCCH (CCEsubset) candidates to be searched by UA 10 at each aggregation level. InUA-specific search space 114, at aggregation level 1 the search space is6 CCEs with a total of 6 PDCCH candidates. At aggregation level 2 thesearch space is 12 CCEs with a total of 6 PDCCH candidates. Ataggregation level 4 the search space is 8 CCEs with 2 PDCCH candidates,and at aggregation level 8 the search space is 16 CCEs with 2 PDCCHcandidates. In common search space 112, at aggregation level 4 thesearch space is 16 CCEs with 4 PDCCH candidates and at aggregation level8 the search space is 16 CCEs with 2 PDCCH candidates.

Generally, by using different ones of the aggregation levels shown inFIG. 4 the reliability of a PDCCH transmission may be set for anintended UA. The set of PDCCH candidates to be monitored by a UA aredefined in terms of search spaces, where a search space S_(k) ^((L)) ataggregation levels 1, 2, 4, or 8 is defined by a set of PDCCHcandidates. The CCEs corresponding to PDCCH candidate m of the searchspace S_(k) ^((L)) may be given by the equation:

$\begin{matrix}{{L \cdot \left\{ {\left( {Y_{k} + m} \right){mod}\left\lfloor \frac{N_{{CCE},k}}{L} \right\rfloor} \right\}} + i} & {{Eq}\mspace{14mu} (1)}\end{matrix}$

where Y_(k) (Y_(k) may be calculated as described in Section 9.1.1 of TS36.213) is the random number to define a UE specific search space, L isthe aggregation level, and i=0, . . . , L−1 and m=0, . . . , M^((L))−1.M^((L)) is the number of PDCCH candidates to monitor in a given searchspace.

In the case of carrier aggregation, a control-channel structure isallocated to each carrier for distributing DCI control messages. FIGS. 5a and 5 b illustrate two exemplary PDCCH design options for implementinga control-channel for two or more carriers for carrier aggregation. InFIG. 5 a each carrier f1 and f2 is allocated a separate PDCCH region.Accordingly, DCI control messages relating to carrier f1 are distributedvia PDCCH region 130 and DCI control messages relating to carrier f2 aredistributed via PDCCH region 132. Although being relativelystraight-forward to implement, the PDCCH structure of FIG. 5 a requiresthe allocation of substantial resources on each carrier and does notallow for cases when a particular carrier does not have a PDCCH region.If the PDCCH region for multiple carriers is reserved on a singlecarrier, then the other carrier will be configured to transmit onlyPDSCH without the control region, which will increase the bandwidthefficiency of PDSCH transmission. In addition, the coverage of eachcarrier may be different. Also, in some cases, it may be desirable totransmit control on a single carrier in order to simplify UAimplementation. Accordingly, in many cases, a particular carrier may notimplement or make available a PDCCH region.

FIG. 5 b illustrates an alternative PDCCH region design option where onePDCCH region may be configured to distribute DCI control messages forthe carrier on which the PDCCH is transmitted in addition to zero ormore other carriers. In FIG. 5 b, DCI control messages relating tocarrier f1 are distributed via PDCCH region 136. In addition, PDCCHregion 136 on carrier f1 may be configured to distribute DCI controlmessages relating to carrier f2 and/or additional carriers (notillustrated). Although it may be possible to implement the PDCCH designoption illustrated in FIG. 5 b using a new DCI field that indicates thePDSCH/PUSCH carrier to which the DCI control message relates, such asolution is not desirable as it would modify or increase the number ofexisting DCI formats.

The present system facilitates the sharing of a single control channelsuch as a Physical Downlink Control CHannel (PDCCH) region amongst twoor more carriers that allows DCI control messages distributed via onePDCCH region on a first carrier to determine resource allocations oneach of the two or more carriers. Depending upon the networkconfiguration, the present system may be implemented using aconventional DCI control message format. As such, the lengths of theexisting DCI formats, even after implementation of the present system,may remain unchanged. While each solution is described separately below,it should be appreciated that various aspects of the different solutionsmay be combined in at least some embodiments to result in other usefulsolutions.

Solution 1

In one implementation of the present system, the CCEs on a singlecarrier PDCCH region are assigned to different groups, wherein eachgroup is pre-assigned to different carriers of a multi-carrier system.For example, with reference to FIG. 6, PDCCH region 140 is located oncarrier f1. The CCEs of PDCCH region 140 are allocated into two groups,with each group being assigned to either carrier f1 or carrier f2. PDCCHregion 140 includes a first CCE group 142 of PDCCH 140 wherein the CCEgroup 142 is allocated to carrier f1. The first CCE group 142 includesCCEs 0-17 of PDCCH region 140. Similarly, a second CCE group 144 ofPDCCH region 140 is allocated to carrier f2 and includes CCEs 18-35 ofPDCCH region 140. In systems having three or more carriers, the CCEs ona single PDCCH region may be allocated into a number of groups equal tothe number of carriers. Depending upon the network implementation, thenumber of CCEs allocated to each group may be equal, or varying betweenthe carriers.

Referring still to FIG. 6, aggregation levels and search spaces that maybe present within PDCCH region 140 for allocating DCI control messagesbetween carriers f1 and f2 are shown. PDCCH region 140 includes 36 CCEs.CCEs 0-17 are placed into a first group and allocated to carrier f1 (thecarrier containing PDCCH region 140) and CCEs 18-35 are placed into asecond group and allocated to carrier f2. Using PDCCH region 140, accessdevice 12 selects one or an aggregation or subset of CCEs to transmit aDCI control message to UA 10. The particular CCE subset selected by theaccess device may depend at least in part on perceived communicationconditions between the access device and the UA. The CCE subset selectedalso determines the carrier on which the DCI control message allocatesresources.

For example, where a high quality communication link is known to existbetween an access device and a UA on carrier f1, the access device maytransmit control messages to the UA via a single one of the CCEs (see146) within the group of CCEs 142 allocated to carrier f1. Where thecarrier f1 link is low quality, the access device may transmit data tothe UA via a subset of two (see 148), four (see 150) or even eight CCEs(see 152) within the group of CCEs 142 allocated to carrier f1, wherethe additional CCEs facilitate a more robust transmission of anassociated DCI message to the UA.

Similarly, where a high quality communication link is known to existbetween an access device and a UA on carrier f1, the access device maytransmit data to the UA via a single one of the CCEs (see 154) withinthe group of CCEs 144 allocated to carrier f2. Since the PDCCH regionfor carrier f2 is transmitted on carrier f1, the channel quality oncarrier f1 should be considered in determining the aggregation level.Where the carrier f1 link is low quality, the access device may transmitdata to the UA via a subset of two (see 156), four (see 158) or eveneight CCEs (see 160) within the group of CCEs 144 allocated to carrierf2, where the additional CCEs facilitate a more robust transmission ofan associated DCI message. The access device may select CCE subsets forDCI message transmission based on many other criteria.

If a UA finds a valid DCI control message format in CCE space 142designated for carrier f1, the UA may conclude that the correspondinggrant is valid for carrier f1. Conversely, if a UE finds a valid DCIformat in CCE space 144 designated for carrier f2, the UE may concludethat the corresponding grant is valid for carrier f2.

In many cases, the total number of CCEs made available on PDCCH region140 may be more or less than 36 depending upon system requirements. Forexample, a high number of CCEs within the PDCCH region may minimizeoccurrences of blocking on the PDCCH, where the access device wishes totransmit to a particular UA during a given subframe, but the accessdevice cannot find a suitable subset of CCEs within the PDCCH region inwhich to place the desired DCI control message. Furthermore, it is notnecessary that the CCEs be evenly distributed between carriers. Forexample, a carrier that is known to have a particular strong orhigh-quality connection between an access device and scheduled UAs maybe allocated less total CCEs within the PDCCH region as it is unlikelythat higher levels of aggregation will be necessary for the carrier.Conversely, carriers with very low-quality connections may be allocateda higher total number of CCEs within the PDCCH region as they will moreoften require high levels of aggregation.

In one implementation, CCE set 142 allocated to carrier f1 is signaledusing Rel-8 signaling Physical Control Format Indicator Channel (PCFICH)and CCE set 144 allocated to carrier f2 is signaled using an alternativesignaling method. In that case, Rel-8 UAs may not be served by CCE set144.

In another implementation, the entire CCE space (including CCE sets 142and 144) is signaled using Rel-8 signaling to Rel-8 UAs using thePCFICH, and CCE sets 142 and 144 are signaled as two entities to Rel-10UAs using Rel-10 signaling. For example, RRC signaling can be used toindicate CCE sets 142 and 144. In that case, Rel-8 UAs may span theentire PDCCH space for a single grant, while a single grant for Rel-10UAs is located in either CCE set 142 or CCE set 144. In both cases, thesolution may be transparent to Rel-8 UAs, because the UAs use the samePDCCH search procedure as currently defined, and the access device mayensure that a particular grant is located in the proper place for eachUA.

In some cases, it may be difficult to define a sufficiently large PDCCHspace using Rel-8 techniques to accommodate multiple carrier operation.For example, if more than 3 Orthogonal Frequency Division Multiplex(OFDM) symbols are needed for the PDCCH, it may be difficult to offsetthe traffic channel (PDSCH) from the control channel (PDCCH). As such,the system or a portion of the system may be implemented in the logicaldomain, where CCE set 142 is defined as in Rel-8 and CCE set 144 uses aparticular set of radio resources, for example a set of physicalresource blocks. This, however, may require that the UA buffer theentire subframe and may therefore eliminate the micro-sleep advantage ofthe existing PDCCH structure.

The first solution described above may not allow trunking between PDCCHregion 140 CCE subsets 142 and 144 for carrier f1 and carrier f2, andtherefore may result in a higher blocking rate compared to a completelycommon PDCCH space. Therefore, it may be desirable to use a common setof CCEs to make allocations on both carriers f1 and f2 without changingthe Rel-8 DCI formats. In addition, it may be difficult to reserve thesearch space for each carrier, especially at larger aggregation levels.

Signaling may be implemented to instruct each UA how to map a set ofCCEs to a particular carrier. In some cases, broadcast signaling may beused to divide the PDCCH region into CCE groups. For example, referringagain to FIG. 6, broadcast signaling may be used to indicate that CCEset 142 corresponds to CCEs 0-17 and CCE set 144 corresponds to CCEs18-35.

After the CCE sets are configured, the access device may indicate whichcarriers correspond to which CCE set. Additionally, the access devicemay indicate a carrier index within each CCE set. For example, where CCEset 142 is referred to as CCE set “0” and is used for three carriers(not as in FIG. 6) and CCE set 144 is referred to as CCE set “1” and isused for one carrier, example signaling is illustrated in the followingtable:

TABLE 1 Carrier Carrier Index Index CCE Set Within CCE Set 0 0 0 1 0 1 20 2 3 1 0In this case, the DCI messages may be modified to indicate the carrierindex within the CCE set, or one of the solutions described below can beused to indicate the carrier.

If there is only one defined CCE set, as in FIG. 6, the carrier indexwithin the CCE set may be equal to the carrier index, in which casesignaling may not be necessary.

Solution 2

In other implementations, CCEs can be shared among multiple componentcarriers provided that a first PDCCH DCI control message candidate for afirst carrier at a particular aggregation level does not overlap with asecond PDCCH DCI control message candidate for a second carrier at thesame aggregation level. Referring to FIG. 7, carriers f1 and f2 each maybe allocated resources by any of the CCEs (in this example, a total of36 CCEs numbered 0-35) available on the carrier f1 PDCCH region 162. Todifferentiate CCE allocations for carrier f1 and carrier f2, PDCCH 162candidates for each non-anchor carrier at an aggregation level areshifted by a number of CCEs allocated on the anchor carrier relative tothe position of each PDCCH candidate on the anchor carrier.

In FIG. 7, aggregation levels and search spaces that may be presentwithin PDCCH region 162 for allocating DCI control messages betweencarriers f1 and f2 are illustrated, where the DCI control messages forcarriers f1 and f2 may be distributed throughout PDCCH region 162. InFIG. 7, DCI control messages for carriers f1 and f2 each may beallocated one or more of CCEs numbered 0-35 (i.e., any of the CCEsavailable on PDCCH region 162). To differentiate allocations for carrierf1 and carrier f2, the PDCCH candidates for carrier f2 are shiftedrelative to the position of the CCEs allocated to the anchor carrier(e.g., carrier f1).

For example, in FIG. 7, the PDCCH candidates for aggregation level 1 forcarrier f2 are shifted relative to the PDCCH candidates for carrier f1by the number of CCEs allocated to the anchor carrier at aggregationlevel 1. In FIG. 7, six CCEs starting with PDCCH candidate 166 have beenallocated to the anchor carrier (carrier f1). The starting CCE 164 forthe carrier f2 PDCCH candidates, therefore, is shifted from the samestarting position as those on the anchor carrier by the number of CCEsallocated to the anchor carrier—in this case 6. As such, the startingpoint for PDCCH candidate 164 is shifted 6 CCEs to the right.

Similarly, referring still to FIG. 7, there are six PDCCH or CCE subsetcandidates for AL2 and carrier f1 that start with candidate 168. Becausethere are six PDCCH candidates on AL2, the first 170 of six PDCCHcandidates for carrier f2 on AL2 is shifted by six candidates as shown.

A similar process may be repeated to specify and issue PDCCH candidatesallocated amongst the carriers at each aggregation level. The algorithmmay also be applied as additional carriers are added to the system.PDCCH candidates for a third carrier, for example, would be shifted tothe right by the number of PDCCH candidates allocated to both carriersf1 and f2. Similarly, PDCCH candidates for a fourth carrier would beshifted to the right by the number of PDCCH candidates allocated tocarriers f1, f2, and f3.

If UA 10 finds a valid DCI control message format at a particularaggregation level, the UA 10 can determine to which carrier the grant isallocated based upon the CCEs used to transmit the DCI message. If theCCEs used to transmit the DCI message are within those allocated to afirst carrier, the grant is for resources on the first carrier. If,however, the CCEs are included within the set allocated to a secondcarrier, the grant is for resources on the second carrier, and so on.

In FIG. 7, for aggregation level 4 and aggregation level 8, only asingle carrier (e.g., the anchor carrier) may overlap with the commonsearch space. As such, special handling of the AL4 and AL8 regions ofPDCCH 162 is required. In the example shown in FIG. 7, while twocandidates 165 and 167 exist for carrier f2 at AL4, there are zerocandidates for f2 at AL8 because the remaining candidates are used foreither the UA specific search space or the common search space oncarrier f1.

In another implementation, the UA retrieves all DCI control messagesdistributed at a first aggregation level and determines the carrierassociated with each control message based upon the total number of DCIcontrol messages at that aggregation level assuming the control messagesare evenly distributed amongst the carriers. For example, if there are 6total DCI control messages distributed at aggregation level 1, and UA 10knows there are two carriers being served by the PDCCH, the UA maydetermine that the first three control messages allocate resources oncarrier f1 and the second three control messages allocate resources oncarrier f2. In other words, the system may be configured to evenlydistribute the PDCCH candidates amongst the carriers and also to issuethe candidates in the same ordering as that of the carriers. In the caseof three carriers, for example, the first third of the control messageswould allocate resources on carrier f1, the second third on carrier f2and the final third on carrier f3. This process may be repeated at allaggregation levels for any number of carriers.

In some cases, it may be difficult to define a sufficiently large PDCCHspace using Rel-8 techniques to accommodate multiple carrier operation.Because a common search space may be shared between Rel-8 and Rel-10UEs, the search space may be signaled using Rel-8 signaling such as thePCFICH. As a result, the search space may be limited to a total of 3OFDM symbols (or 4 OFDM symbols for a carrier bandwidth of 1.4 MHz,although such a narrow bandwidth is unlikely to be applied for carrieraggregation).

In FIG. 7, the PDCCH candidates for carrier f2 are located next to thePDCCH candidates for carrier f1. This is one positioning algorithm, andit should be understood that any positioning algorithm can be used. Forexample, the PDCCH candidates for carrier f2 may be locatedpseudo-randomly within the PDCCH, similar to the process used for thePDCCH candidates for carrier f1. In case a PDCCH candidate for carrierf1 overlaps with a PDCCH candidate for carrier f2, one carrier must begiven priority. For example, in case of overlap, the PDCCH candidatescan be known at the UA 10 and access device 12 to correspond to carrierf1.

Solution 3

In another implementation, for a particular aggregation level, thestarting CCE for PDCCH candidates allocated for each carrier at eachaggregation level is shifted based upon the number of CCEs in the nextsmaller aggregation level. FIG. 8 illustrates PDCCH 180 wherein, foreach aggregation level, the PDCCH candidates for a particular carriermay be shifted by a multiple of the number of CCEs in the next smalleraggregation level. For example, at one aggregation level and for twocarriers, the DCI control messages for the second carrier may be offsetfrom the control messages for the first carrier by a number of CCEsequal to the number of CCEs that are aggregated into each PDCCHcandidate at the next lower aggregation level. Note that the offset foraggregation level 1 is a unique case as there is no aggregation levellower than 1. In that case, the offset for aggregation level may be setto any integer (e.g., an offset of 6 is illustrated in FIG. 8).

Referring still to FIG. 8 for a specific example, the starting CCE forthe aggregation level 2 PDCCH candidate 184 for carrier f2 is shifted byone CCE (equal to the number of aggregated CCEs in the next smalleraggregation level) relative to the PDCCH candidate 182 for carrier f1.Similarly, the PDCCH candidates 188 for aggregation level 4 for carrierf2 are shifted by two CCEs (equal to the number of aggregated CCEs inthe next smaller aggregation level) relative to the PDCCH candidates 186for carrier f1, and so on.

By shifting PDCCH candidates for different frequencies at any givenaggregation level by the number of CCEs in each PDCCH candidate at alower aggregation level, the PDCCHs at the different frequencies at eachaggregation level will not precisely overlap and therefore the CCEsubset candidates are unique.

Here it should be appreciated that this third solution may begeneralized such that any offset which is less than the number Q of CCEsthat make up a PDCCH candidate at the same aggregation level may beused. More broadly, the primary restriction on the offset is that it isnot an integer multiple of Q. For instance, at aggregation level AL4 inFIG. 8, the offset shown is equal to two CCEs. That offset may bechanged to one CCE or three CCEs (i.e., Q−1) to achieve a similaraffect. Similarly, the four CCE offset shown in FIG. 8 for AL8 may beanywhere from one CCE to seven CCEs (i.e., again Q−1 where Q is thenumber of CCEs in each AL8 CCE subset candidate).

More broadly, the primary restriction on the offset shift may be that itis not an integer multiple of the number of CCEs that make up a PDCCHcandidate at the same aggregation level in at least some embodiments.

Solution 4

Referring to FIG. 9, in yet one other embodiment, the carrier for aparticular PDCCH candidate may be calculated by the CCE index of thePDCCH candidate. For example, assuming the number of configured carriersis N, the carrier index for a particular PDCCH candidate may bedetermined by the following equation:

Carrier Index=(I _(cce) /L)MOD N+1   Eq (2)

where I_(cce) is the index of the first CCE in a specific PDCCHcandidate and L is the currently considered aggregation level. In FIG.9, for example, the carrier index for PDCCH candidate 202 may bedetermined using Eq (2). PDCCH candidate 202 has an I_(cce) of 4, anaggregation level of 1. PDCCH includes 2 carriers, so the carrier forPDCCH candidate 202 is equal to (4/1) MOD 2+1=4 MOD 2+1=0+1=1.Similarly, PDCCH candidate 204 has an I_(cce) of 12, and an aggregationlevel of 4. Accordingly, the carrier for PDCCH candidate 204 is equal to(12/4) MOD 2+1=3 MOD 2+1=1 +1=2. In this manner, the carrier assigned toeach PDCCH candidate in FIG. 9 may be calculated by the UA. As such, insome implementations, the present system interdigitates PDCCH candidatesfor each carrier at a particular aggregation level.

To guarantee that a UA achieves an unique carrier index with equation(2), it is necessary to increase the number of PDCCH candidates as afunction of the number of configured carriers as shown in FIG. 10. InFIG. 10 a table is provided that shows aggregation levels forUA-specific space and the minimum required size of the search space foreach aggregation level in number of CCEs. At aggregation level 1 theminimum search space is N CCEs where N is the number of carriers. Ataggregation level 2 the minimum search space is 2*N CCEs. At aggregationlevel 4 the minimum search space is 4*N CCEs, and at aggregation level 8the minimum search space is 8*N CCEs. That is, the minimum search spacesize could be specified as AL*N CCEs, where AL is the aggregation level(1, 2, 4, or 8) and N is the number of carriers.

In other embodiments, in the case of carrier aggregation, where anaccess device communicates with several UAs, blocking may occur whereall of the PDCCH candidates associated with one of the UAs (at one ormore of the aggregation levels) are currently being used and a delayoccurs in transmitting a grant to one or more of the UAs. For thisreason, it has been recognized that in the case of carrier aggregation,in at least some cases it will be useful to be able to increase the sizeof the CCE search space and the number of PDCCH candidates in caseswhere a UA is capable of blind decoding an increased number ofcandidates. For instance, in some cases, it may be useful to increasethe CCE search space size and number of PDCCH candidates as a functionof the number of configured carriers. One exemplary way to increase thesearch space size and number of PDCCH candidates as a function of thenumber of configured carriers is illustrated in FIG. 17 where, forinstance, max(N,6) means the maximum of the number of carriers and 6 isselected as the size of the search space in CCEs for aggregation level1, 2×max(N,6) means the maximum of two times the number of carriers and12, and so on. Thus, for instance, where the number of configuredcarriers is 4, the search space in CCEs is 32 (e.g., 8×max(N,2) where Nis 4) and the number of PDCCH candidates is 4 (e.g., max(N,2) where N is4) so that there will be four candidates where each candidate includes 8CCEs.

In order to receive the downlink DCI and the uplink DCI simultaneously,the number of PDCCH candidates can be increased by two times the numberof configured carriers as shown in FIG. 18.

In another embodiment, a larger number of PDCCH candidates can be usedinstead of the number of PDCCH candidates used in the LTE Rel-8 systemwhen carrier aggregation is configured regardless of number of actualconfigured carriers. FIG. 19 shows one exemplary approach where M1, M2,M3 and M4 represent the number of PDCCH candidates for aggregationlevels 1, 2, 4, and 8, respectively, and where M1, M2, M3 and M4 shouldbe greater than or equal to the number of PDCCH candidates used in LTERel-8 respectively. These values can be signaled or predefined in thespecification. In at least some embodiments the same value can be usedfor M1, M2, M3 and M4 or different values can be used. In FIG. 19 notethat where only a single carrier is configured, the search space sizeand number of PDCCH candidates are identical to the space size andcandidate numbers in the Rel 8 system. Thus, here again, the number ofconfigured carriers affects the search space size and the number ofPDCCH candidates.

FIGS. 10, 17, 18 and 19 shows several different ways to extend the UEspecific search space, but the techniques can also apply to the commonsearch space if the PDCCH transmitted in the common search space istransmitted on a different carrier from the carrier on which PDSCH/PUSCHare transmitted.

The number of carriers for PDSCH transmission, and the number ofcarriers for PUSCH transmission can be different depending on the eNBconfiguration. In this case, N can be the larger number of carriers.

In another embodiment, referring to FIG. 20, a first set of PDCCHcandidate sizes (A1, A2, A3, and A4) may be used for single carrieroperation (N=1) and a second set of PDCCH candidate sizes (C1, C2, C3,and C4) may be used for carrier aggregation, wherein the second set ofPDCCH candidate sizes (C1, C2, C3, C4) are defined using a functionwhich includes the first set of PDCCH candidate sizes (A1, A2, A3, A4)and a scaling parameter (B1, B2, B3, and B4) multiplied by the number ofcarriers (N) minus 1. In at least some embodiments, the first set ofPDCCH candidate sizes (i.e., A1, A2, A3, A4) equals those used in LTERel-8.

This scheme may be further generalized so that a single set of PDCCHcandidates may be dedicated to a particular set of carriers in anon-uniform manner. For example, for two carriers, one carrier may beallocated 6 PDCCH candidates and the other carrier may be allocated 3PDCCH candidates. Alternatively, equations may be employed so that thelocations of the PDCCH candidates for a particular aggregation level arerandom for each carrier. This may be implemented, for example, by addinga carrier index field to the equations found in 3GPP TS 36.213, v8.6.0,March 2009.

In some cases, depending on the size of the PDCCH, it may be possiblefor PDCCH candidates for more than one carrier to collide. In that case,the PDCCH candidate may be allocated to a particular carrier, forexample the carrier with the lowest carrier index (e.g. the anchorcarrier).

In some cases, the search space size and number of PDCCH candidatesincrease with the number of carriers up to a certain number of carriersand then maintain a constant value as more carriers are added. Forexample, for 1, 2, 3, 4, 5 carriers respectively, considering N=1, thenumber of PDCCH candidates could be 6, 10, 14, 18, 18. In this case, noadditional PDCCH candidates are used in the transition between 4 and 5carriers.

The above embodiments of the present system may be implementedseparately or in combination.

Solution 5

In some implementations of the present system, the anchor carrier'sC-RNTI or the RNTI of each UA may be used to determine the allocation ofPDCCH candidates amongst carriers in the UE-specific search space. Inthe following examples, the search space may be the same size orexpanded relative to Rel-8.

Multiple RNTIs may be assigned to a UA with one RNTI being assigned foreach carrier. For example, for a system using two carriers, a UA may beassigned a first RNTI associated with a first carrier and a second RNTIassociated with a second carrier. If the access device wishes toallocate resources on the second carrier to the first UA, the accessdevice uses the second RNTI of the UA when encoding the DCI controlmessage. Similarly, if the access device wishes to allocate resources onthe first carrier to the UA, the access device uses the first RNTI ofthe UA when encoding the DCI control message. As such, the UA candetermine which carrier the control message allocates services on byattempting to decode the message using both RNTIs. The number of theRNTI that successfully decodes the control message tells the UA thecarrier on which the control message allocates resources.

For example, after receiving a PDCCH candidate, each UA may attemptblind decoding of the candidate. After blind decoding, the CRCscrambling of the PDCCH candidate is compared against all of the UA'sassigned RNTI values. If one of the RNTI can be used to successfullydescramble the PDCCH candidate, the RNTI used to perform thedescrambling identifies the particular carrier associated with the DCIcontrol message of the PDCCH candidate. Alternatively, different CRCmasks may be used for each carrier to achieve a similar functionality.

In another implementation, the modulation symbols or Resource ElementGroups (REGs) within a PDCCH candidate are rotated (or otherwise havetheir order varied) as an indication of which carrier the PDCCHcandidate allocates resources. For example, after generating the LogLikelihood Ratios (LLRs) for a particular PDCCH candidate, a UA attemptsto blind decode the PDCCH candidate using the standard approach (andstandard configuration of the REGs).

If the decoding is successful, the PDCCH candidate is allocated tocarrier f1. If the decoding fails, the UA is configured to shuffle theLLRs (corresponding to the modulation symbols) of the REGs into analternate order accordingly to a pre-determined algorithm and attemptblind decoding again. If the blind decoding using the first alternateordering works, the PDCCH candidate is allocated to carrier f2. Theshuffling algorithm may be implemented a second, third or fourth time,for example, to identify third, fourth and fifth carriers. In thisexample, the standard order and any pre-defined alternate orderings forthe LLR correspond to different carriers. In some cases, two or moredifferent ordering configurations may be defined for the REGs, allowingthe REG ordering to indicate allocation of a PDCCH candidate to one oftwo or more carriers.

As an example, FIGS. 11 a-11 c illustrate REG reordering, wherein theREG ordering may be used to distinguish amongst carriers associated witha PDCCH candidate. FIG. 11 a illustrates REGs that may be defined foraggregation level 1. FIG. 11 b illustrates an example order of the REGsof FIG. 11 a for identifying carrier f1. FIG. 11 c illustrates anexample order of the REGs of FIG. 11 a for identifying carrier f2. Ataggregation level 1, nine REGs (as shown in FIG. 11 a) may be used toconstruct one CCE which may then be blind decoded to determine whether avalid DCI control message is present. A first REG ordering is used forcarrier f1. If blind decoding of the PDCCH candidate is successful usingthe ordering of FIG. 11 b, the UA 10 determines that the PDCCH candidateis allocated to carrier f1. However, if blind decoding fails, the REGsmay be reordered in accordance with FIG. 11 c and a second blinddecoding may be attempted by the UA. If the blind decoding issuccessful, UA 10 determines that the PDCCH candidate is allocated tocarrier f2. If, however, that blind decoding is also unsuccessful, UA 10may determine that the PDCCH candidate is invalid (e.g., allocated toanother UA), or is allocated to another carrier.

In FIGS. 11 b and 11 c, a reversal of the individual REGs is shown todistinguish PDCCH candidates allocated to carrier f2 from thoseallocated to carrier f1. In other implementations, however, otherreordering algorithms may be implemented. In one example, the individualresource elements or modulation symbols within each REG are reordered toimplicitly signal a different carrier. For example, the position of aspecific number or combination of numbers within the REG may indicatethe carrier.

Alternatively, for aggregation levels higher than aggregation level 1,the ordering of the CCEs that make up a potential PDCCH candidate couldbe varied with their ordering indicating the carrier to which the PDCCHcandidate is allocated. An example of such an approach is shown in FIG.12. FIG. 12 shows an example construction of PDCCH candidates for eachof carriers f1 and f2 at aggregation levels 2, 4, and 8.

For each potential PDCCH candidate, blind decoding on the aggregatedCCEs in the currently specified ordering (e.g., according to the LTEspecification) is first attempted. If the blind decoding is successful,it may indicate that the PDCCH candidate is allocated to carrier f1. Ifblind decoding fails, then the CCEs are reordered (FIG. 12 illustrates arotation of the CCEs by half the amount of the current aggregationlevel, but other CCE reorderings may also be possible) and a secondblind decoding is performed. If this blind decoding is successful, itmay indicate that the PDCCH candidate is allocated to carrier f2. Thisapproach would not work for aggregation level AL1, because this approachrequires multiple CCEs being used to construct a PDCCH candidate.

Thus, in FIG. 12, at AL2 and carrier f1, CCEs 0 and 1 are processed inthe conventional order 0 followed by 1. If decoding is successful, theDCI message corresponds to carrier f1. The UA 10 also attempts to decodethe CCEs in the reverse order 1 followed by 0 where successful decodingresults in a DCI message corresponding to carrier f2. The UA 10 alsoattempts to decode CCEs 0, 1, 2 and 3 in the conventional order forcarrier f1 and in the order 2, 3, 0, 1 for carrier f2 at level AL4 andCCEs 0, 1, 2, 3, 4, 5, 6 and 7 in the conventional order for carrier f1and in the order 4, 5, 6, 7, 0, 1, 2, and 3 for carrier f2 at level AL8.

Finally, a reserved bit may be used in an existing DCI format or thedefinition of one or more existing DCI format fields may be changed toallow the DCI control message to explicitly indicate to which carrierthe grant corresponds.

The present system provides a multi-carrier control structure, whereinthe PDCCH on one carrier may include PDCCH candidates that allocateresources amongst two or more carriers. In one implementation, thepresent system does not require modifications to existing Rel-8 DCIcontrol message formats, and does not change the lengths of the existingRel-8 DCI formats.

Moving forward, in LTE-A for example, in addition to the existing DCIformats, new DCI formats may be proposed to support new features (e.g.,8×8 MIMO and CoMP). As such, explicit bits may be added into any new DCIformats to signal the carriers. Even so, it may still be beneficial toimplement the implicit PDCCH allocation of carriers as described in thepresent system. First, Rel-8 modes such as transmit diversity andopen-loop SM may still be considered as fallback mode or transmissionmode for a high mobility UA in an LTE-A system. Accordingly, acorresponding Rel-8 DCI format such as format 1A may still be used insuch a system. Secondly, if explicit bits for identifying a carrier aredefined in new DCI formats, say 3 bits, then any such bits may need toalways be transmitted, and may often be wasted when only two carriersare aggregated, or there is no carrier aggregation. In that case, if theexplicit bits vary, say from 0-3 bits, then such an implementation mayincrease blind decoding. In contrast, if the number of any such explicitbits is specified semi-statically for different carrier aggregationdeployment, then the numbers of variations of DCI formats may increasesubstantially.

FIG. 13 illustrates a wireless communications system including anembodiment of UA 10. UA 10 is operable for implementing aspects of thedisclosure, but the disclosure should not be limited to theseimplementations. Though illustrated as a mobile phone, the UA 10 maytake various forms including a wireless handset, a pager, a personaldigital assistant (PDA), a portable computer, a tablet computer, alaptop computer. Many suitable devices combine some or all of thesefunctions. In some embodiments of the disclosure, the UA 10 is not ageneral purpose computing device like a portable, laptop or tabletcomputer, but rather is a special-purpose communications device such asa mobile phone, a wireless handset, a pager, a PDA, or atelecommunications device installed in a vehicle. The UA 10 may also bea device, include a device, or be included in a device that has similarcapabilities but that is not transportable, such as a desktop computer,a set-top box, or a network node. The UA 10 may support specializedactivities such as gaming, inventory control, job control, and/or taskmanagement functions, and so on.

The UA 10 includes a display 702. The UA 10 also includes atouch-sensitive surface, a keyboard or other input keys generallyreferred as 704 for input by a user. The keyboard may be a full orreduced alphanumeric keyboard such as QWERTY, Dvorak, AZERTY, andsequential types, or a traditional numeric keypad with alphabet lettersassociated with a telephone keypad. The input keys may include atrackwheel, an exit or escape key, a trackball, and other navigationalor functional keys, which may be inwardly depressed to provide furtherinput function. The UA 10 may present options for the user to select,controls for the user to actuate, and/or cursors or other indicators forthe user to direct.

The UA 10 may further accept data entry from the user, including numbersto dial or various parameter values for configuring the operation of theUA 10. The UA 10 may further execute one or more software or firmwareapplications in response to user commands. These applications mayconfigure the UA 10 to perform various customized functions in responseto user interaction. Additionally, the UA 10 may be programmed and/orconfigured over-the-air, for example from a wireless base station, awireless access point, or a peer UA 10.

Among the various applications executable by the UA 10 are a webbrowser, which enables the display 702 to show a web page. The web pagemay be obtained via wireless communications with a wireless networkaccess node, a cell tower, a peer UA 10, or any other wirelesscommunication network or system 700. The network 700 is coupled to awired network 708, such as the Internet. Via the wireless link and thewired network, the UA 10 has access to information on various servers,such as a server 710. The server 710 may provide content that may beshown on the display 702. Alternately, the UA 10 may access the network700 through a peer UA 10 acting as an intermediary, in a relay type orhop type of connection.

FIG. 14 shows a block diagram of the UA 10. While a variety of knowncomponents of UAs 110 are depicted, in an embodiment a subset of thelisted components and/or additional components not listed may beincluded in the UA 10. The UA 10 includes a digital signal processor(DSP) 802 and a memory 804. As shown, the UA 10 may further include anantenna and front end unit 806, a radio frequency (RF) transceiver 808,an analog baseband processing unit 810, a microphone 812, an earpiecespeaker 814, a headset port 816, an input/output interface 818, aremovable memory card 820, a universal serial bus (USB) port 822, ashort range wireless communication sub-system 824, an alert 826, akeypad 828, a liquid crystal display (LCD), which may include a touchsensitive surface 830, an LCD controller 832, a charge-coupled device(CCD) camera 834, a camera controller 836, and a global positioningsystem (GPS) sensor 838. In an embodiment, the UA 10 may include anotherkind of display that does not provide a touch sensitive screen. In anembodiment, the DSP 802 may communicate directly with the memory 804without passing through the input/output interface 818.

The DSP 802 or some other form of controller or central processing unitoperates to control the various components of the UA 10 in accordancewith embedded software or firmware stored in memory 804 or stored inmemory contained within the DSP 802 itself. In addition to the embeddedsoftware or firmware, the DSP 802 may execute other applications storedin the memory 804 or made available via information carrier media suchas portable data storage media like the removable memory card 820 or viawired or wireless network communications. The application software maycomprise a compiled set of machine-readable instructions that configurethe DSP 802 to provide the desired functionality, or the applicationsoftware may be high-level software instructions to be processed by aninterpreter or compiler to indirectly configure the DSP 802.

The antenna and front end unit 806 may be provided to convert betweenwireless signals and electrical signals, enabling the UA 10 to send andreceive information from a cellular network or some other availablewireless communications network or from a peer UA 10. In an embodiment,the antenna and front end unit 806 may include multiple antennas tosupport beam forming and/or multiple input multiple output (MIMO)operations. As is known to those skilled in the art, MIMO operations mayprovide spatial diversity which can be used to overcome difficultchannel conditions and/or increase channel throughput. The antenna andfront end unit 806 may include antenna tuning and/or impedance matchingcomponents, RF power amplifiers, and/or low noise amplifiers.

The RF transceiver 808 provides frequency shifting, converting receivedRF signals to baseband and converting baseband transmit signals to RF.In some descriptions a radio transceiver or RF transceiver may beunderstood to include other signal processing functionality such asmodulation/demodulation, coding/decoding, interleaving/deinterleaving,spreading/despreading, inverse fast Fourier transforming (IFFT)/fastFourier transforming (FFT), cyclic prefix appending/removal, and othersignal processing functions. For the purposes of clarity, thedescription here separates the description of this signal processingfrom the RF and/or radio stage and conceptually allocates that signalprocessing to the analog baseband processing unit 810 and/or the DSP 802or other central processing unit. In some embodiments, the RFTransceiver 808, portions of the Antenna and Front End 806, and theanalog baseband processing unit 810 may be combined in one or moreprocessing units and/or application specific integrated circuits(ASICs).

The analog baseband processing unit 810 may provide various analogprocessing of inputs and outputs, for example analog processing ofinputs from the microphone 812 and the headset 816 and outputs to theearpiece 814 and the headset 816. To that end, the analog basebandprocessing unit 810 may have ports for connecting to the built-inmicrophone 812 and the earpiece speaker 814 that enable the UA 10 to beused as a cell phone. The analog baseband processing unit 810 mayfurther include a port for connecting to a headset or other hands-freemicrophone and speaker configuration. The analog baseband processingunit 810 may provide digital-to-analog conversion in one signaldirection and analog-to-digital conversion in the opposing signaldirection. In some embodiments, at least some of the functionality ofthe analog baseband processing unit 810 may be provided by digitalprocessing components, for example by the DSP 802 or by other centralprocessing units.

The DSP 802 may perform modulation/demodulation, coding/decoding,interleaving/deinterleaving, spreading/despreading, inverse fast Fouriertransforming (IFFT)/fast Fourier transforming (FFT), cyclic prefixappending/removal, and other signal processing functions associated withwireless communications. In an embodiment, for example in a codedivision multiple access (CDMA) technology application, for atransmitter function the DSP 802 may perform modulation, coding,interleaving, and spreading, and for a receiver function the DSP 802 mayperform despreading, deinterleaving, decoding, and demodulation. Inanother embodiment, for example in an orthogonal frequency divisionmultiplex access (OFDMA) technology application, for the transmitterfunction the DSP 802 may perform modulation, coding, interleaving,inverse fast Fourier transforming, and cyclic prefix appending, and fora receiver function the DSP 802 may perform cyclic prefix removal, fastFourier transforming, deinterleaving, decoding, and demodulation. Inother wireless technology applications, yet other signal processingfunctions and combinations of signal processing functions may beperformed by the DSP 802.

The DSP 802 may communicate with a wireless network via the analogbaseband processing unit 810. In some embodiments, the communication mayprovide Internet connectivity, enabling a user to gain access to contenton the Internet and to send and receive e-mail or text messages. Theinput/output interface 818 interconnects the DSP 802 and variousmemories and interfaces. The memory 804 and the removable memory card820 may provide software and data to configure the operation of the DSP802. Among the interfaces may be the USB interface 822 and the shortrange wireless communication sub-system 824. The USB interface 822 maybe used to charge the UA 10 and may also enable the UA 10 to function asa peripheral device to exchange information with a personal computer orother computer system. The short range wireless communication sub-system824 may include an infrared port, a Bluetooth interface, an IEEE 802.11compliant wireless interface, or any other short range wirelesscommunication sub-system, which may enable the UA 10 to communicatewirelessly with other nearby mobile devices and/or wireless basestations.

The input/output interface 818 may further connect the DSP 802 to thealert 826 that, when triggered, causes the UA 10 to provide a notice tothe user, for example, by ringing, playing a melody, or vibrating. Thealert 826 may serve as a mechanism for alerting the user to any ofvarious events such as an incoming call, a new text message, and anappointment reminder by silently vibrating, or by playing a specificpre-assigned melody for a particular caller.

The keypad 828 couples to the DSP 802 via the interface 818 to provideone mechanism for the user to make selections, enter information, andotherwise provide input to the UA 10. The keyboard 828 may be a full orreduced alphanumeric keyboard such as QWERTY, Dvorak, AZERTY andsequential types, or a traditional numeric keypad with alphabet lettersassociated with a telephone keypad. The input keys may include atrackwheel, an exit or escape key, a trackball, and other navigationalor functional keys, which may be inwardly depressed to provide furtherinput function. Another input mechanism may be the LCD 830, which mayinclude touch screen capability and also display text and/or graphics tothe user. The LCD controller 832 couples the DSP 802 to the LCD 830.

The CCD camera 834, if equipped, enables the UA 10 to take digitalpictures. The DSP 802 communicates with the CCD camera 834 via thecamera controller 836. In another embodiment, a camera operatingaccording to a technology other than Charge Coupled Device cameras maybe employed. The GPS sensor 838 is coupled to the DSP 802 to decodeglobal positioning system signals, thereby enabling the UA 10 todetermine its position. Various other peripherals may also be includedto provide additional functions, e.g., radio and television reception.

FIG. 15 illustrates a software environment 902 that may be implementedby the DSP 802. The DSP 802 executes operating system drivers 904 thatprovide a platform from which the rest of the software operates. Theoperating system drivers 904 provide drivers for the UA hardware withstandardized interfaces that are accessible to application software. Theoperating system drivers 904 include application management services(“AMS”) 906 that transfer control between applications running on the UA10. Also shown in FIG. 15 are a web browser application 908, a mediaplayer application 910, and Java applets 912. The web browserapplication 908 configures the UA 10 to operate as a web browser,allowing a user to enter information into forms and select links toretrieve and view web pages. The media player application 910 configuresthe UA 10 to retrieve and play audio or audiovisual media. The Javaapplets 912 configure the UA 10 to provide games, utilities, and otherfunctionality. A component 914 might provide functionality describedherein.

The UA 10, access device 120, and other components described above mightinclude a processing component that is capable of executing instructionsrelated to the actions described above. FIG. 16 illustrates an exampleof a system 1000 that includes a processing component 1010 suitable forimplementing one or more embodiments disclosed herein. In addition tothe processor 1010 (which may be referred to as a central processor unit(CPU or DSP), the system 1000 might include network connectivity devices1020, random access memory (RAM) 1030, read only memory (ROM) 1040,secondary storage 1050, and input/output (I/O) devices 1060. In somecases, some of these components may not be present or may be combined invarious combinations with one another or with other components notshown. These components might be located in a single physical entity orin more than one physical entity. Any actions described herein as beingtaken by the processor 1010 might be taken by the processor 1010 aloneor by the processor 1010 in conjunction with one or more componentsshown or not shown in the drawing.

The processor 1010 executes instructions, codes, computer programs, orscripts that it might access from the network connectivity devices 1020,RAM 1030, ROM 1040, or secondary storage 1050 (which might includevarious disk-based systems such as hard disk, floppy disk, or opticaldisk). While only one processor 1010 is shown, multiple processors maybe present. Thus, while instructions may be discussed as being executedby a processor, the instructions may be executed simultaneously,serially, or otherwise by one or multiple processors. The processor 1010may be implemented as one or more CPU chips.

The network connectivity devices 1020 may take the form of modems, modembanks, Ethernet devices, universal serial bus (USB) interface devices,serial interfaces, token ring devices, fiber distributed data interface(FDDI) devices, wireless local area network (WLAN) devices, radiotransceiver devices such as code division multiple access (CDMA)devices, global system for mobile communications (GSM) radio transceiverdevices, worldwide interoperability for microwave access (WiMAX)devices, and/or other well-known devices for connecting to networks.These network connectivity devices 1020 may enable the processor 1010 tocommunicate with the Internet or one or more telecommunications networksor other networks from which the processor 1010 might receiveinformation or to which the processor 1010 might output information.

The network connectivity devices 1020 might also include one or moretransceiver components 1025 capable of transmitting and/or receivingdata wirelessly in the form of electromagnetic waves, such as radiofrequency signals or microwave frequency signals. Alternatively, thedata may propagate in or on the surface of electrical conductors, incoaxial cables, in waveguides, in optical media such as optical fiber,or in other media. The transceiver component 1025 might include separatereceiving and transmitting units or a single transceiver. Informationtransmitted or received by the transceiver 1025 may include data thathas been processed by the processor 1010 or instructions that are to beexecuted by processor 1010. Such information may be received from andoutputted to a network in the form, for example, of a computer databaseband signal or signal embodied in a carrier wave. The data may beordered according to different sequences as may be desirable for eitherprocessing or generating the data or transmitting or receiving the data.The baseband signal, the signal embedded in the carrier wave, or othertypes of signals currently used or hereafter developed may be referredto as the transmission medium and may be generated according to severalmethods well known to one skilled in the art.

The RAM 1030 might be used to store volatile data and perhaps to storeinstructions that are executed by the processor 1010. The ROM 1040 is anon-volatile memory device that typically has a smaller memory capacitythan the memory capacity of the secondary storage 1050. ROM 1040 mightbe used to store instructions and perhaps data that are read duringexecution of the instructions. Access to both RAM 1030 and ROM 1040 istypically faster than to secondary storage 1050. The secondary storage1050 is typically comprised of one or more disk drives or tape drivesand might be used for non-volatile storage of data or as an over-flowdata storage device if RAM 1030 is not large enough to hold all workingdata. Secondary storage 1050 may be used to store programs that areloaded into RAM 1030 when such programs are selected for execution.

The I/O devices 1060 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls,voice recognizers, card readers, paper tape readers, printers, videomonitors, or other well-known input/output devices. Also, thetransceiver 1025 might be considered to be a component of the I/Odevices 1060 instead of or in addition to being a component of thenetwork connectivity devices 1020. Some or all of the I/O devices 1060may be substantially similar to various components depicted in thepreviously described drawing of the UA 10, such as the display 702 andthe input 704.

The following 3rd Generation Partnership Project (3GPP) TechnicalSpecifications (TS) are incorporated herein by reference: TS 36.321, TS36.331, and TS 36.300, TS 36.211, TS 36.212 and TS 36.213.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

To apprise the public of the scope of this invention, the followingclaims are made:

1. A method for processing a control channel at a user agent (UA) toidentify at least one of an uplink and a downlink resource allocated bya resource grant within a multi-carrier communication system whereinresource grants are specified by control channel element (CCE) subsets,wherein each CCE subset is a control channel candidate, the methodcomprising the steps of: identifying a number of carriers used tocommunicate with an access device; and based on the number of carriersused to communicate with the access device, identifying a number ofcontrol channel candidates to decode.
 2. The method of claim 1 furtherincluding the step of attempting to decode up to the identified numberof control channel candidates.
 3. The method of claim 1 wherein thereare at least first and second aggregation levels of control channelcandidates where the candidates include first and second differentnumbers of CCEs, respectively, and, wherein, the numbers of controlchannel candidates are different for the first and second aggregationlevels.
 4. The method of claim 1 wherein, when only one carrier is usedto communicate with the UA, a first number of control channel candidatesis identified and, when two or more carriers are used to communicatewith the UA, at least a second number of control channel candidates isidentified where the second number is greater than the first number. 5.The method of claim 1 wherein the identified number of control channelcandidates for multi-carrier operation is at least equal to the numberof candidates for single carrier operation.
 6. The method of claim 1wherein there are several aggregation levels of control channelcandidates and the identified number of control channel candidates formulti-carrier operation corresponding to at least one of the aggregationlevels is the greater of the number of carriers and the number ofcontrol channel candidates for single carrier operation.
 7. The methodof claim 1 wherein there are first, second, third and fourth aggregationlevels of control channel candidates, when only one carrier is used tocommunicate with the UA, the numbers of control channel candidates forthe first, second, third and fourth aggregation levels are A1, A2, A3and A4, respectively, and wherein, A1, A2, A3 and A4 are integersgreater than or equal to zero, and when two or more carriers are used tocommunicate with the UA, the numbers of control channel candidates forthe first, second, third and fourth aggregation levels are a function ofthe number of carriers used to communicate with the UA.
 8. The method ofclaim 7 wherein, when two or more carriers are used to communicate withthe UA, the numbers C1, C2, C3 and C4 of control channel candidates forthe first, second, third and fourth aggregation levels, respectively,are determined by solving the following equations:C1=A1+B1×(N−1)C2=A2+B2×(N−1)C3=A3+B3×(N−1)C4=A4+B4×(N−1) where B1, B2, B3 and B4 are scaling parameters.
 9. Themethod of claim 7 wherein A1, A2, A3 and A4 are 6, 6, 2 and 2,respectively.
 10. An apparatus for processing a control channel at auser agent (UA) to identify at least one of an uplink and a downlinkresource allocated by a resource grant within a multi-carriercommunication system wherein resource grants are specified by controlchannel element (CCE) subset candidates, the apparatus comprising: aprocessor programmed to perform the steps of: identifying the number ofcarriers used to communicate with an access device; and based on thenumber of carriers used to communicate with the access device,identifying a number of control channel candidates to decode.
 11. Theapparatus of claim 10 wherein the processor is further programmed toperform the step of attempting to decode up to the identified number ofcontrol channel candidates.
 12. The apparatus of claim 10 wherein thereare at least first and second aggregation levels of control channelcandidates where the candidates include first and second differentnumbers of CCEs, respectively, and, wherein, the numbers of controlchannel candidates are different for the first and second aggregationlevels.
 13. The apparatus of claim 10 wherein, when only one carrier isused to communicate with the UA, a first number of control channelcandidates is identified and, when two or more carriers are used tocommunicate with the UA, at least a second number of control channelcandidates is identified where the second number is greater than thefirst number.
 14. The method of claim 10 wherein the identified numberof control channel candidates for multi-carrier operation is at leastequal to the number of candidates for single carrier operation.
 15. Themethod of claim 10 wherein there are several aggregation levels ofcontrol channel candidates and the identified number of control channelcandidates for multi-carrier operation corresponding to at least one ofthe aggregation levels is the greater of the number of carriers and thenumber of control channel candidates for single carrier operation. 16.The apparatus of claim 10 wherein there are first, second, third andfourth aggregation levels of control channel candidates, when only onecarrier is used to communicate with the UA, the numbers of controlchannel candidates for the first, second, third and fourth aggregationlevels are A1, A2, A3 and A4, respectively, and wherein, A1, A2, A3 andA4 are integers greater than or equal to zero, and when two or morecarriers are used to communicate with the UA, the numbers of controlchannel candidates for the first, second, third and fourth aggregationlevels are a function of the number of carriers used to communicate withthe UA.
 17. The apparatus of claim 16 wherein, when two or more carriersare used to communicate with the UA, the numbers C1, C2, C3 and C4 ofcontrol channel candidates for the first, second, third and fourthaggregation levels, respectively, are determined by solving thefollowing equations:C1=A1+B1×(N−1)C2=A2+B2×(N−1)C3=A3+B3×(N−1)C4=A4+B4×(N−1) where B1, B2, B3 and B4 are scaling parameters.
 18. Theapparatus of claim 16 wherein A1, A2, A3 and A4 are 6, 6, 2 and 2,respectively.